Electrochemical test sensor

ABSTRACT

An electrochemical test sensor for detecting the concentration of an analyte in a fluid sample. The electrochemical test sensor includes a housing that has a first end and a second opposing end. The housing includes an opening at the first end to receive a fluid test sample. An electrode assembly includes a substrate, a working electrode, a counter electrode and a reagent. The substrate has a first surface and an opposing second surface. The working electrode is disposed on the first surface of the substrate, and the counter electrode is disposed on the second surface of the substrate. The electrode assembly is positioned within the housing to define a reaction channel. The electrochemical test sensor may be used with a removable lancet mechanism or integrated within a lancet mechanism to form one integral unit.

REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/240,619, filed Sep. 8, 2009, and entitled “ElectrochemicalTest Sensor,” which is incorporated herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to test sensors, and morespecifically to an electrochemical test sensor that is adapted todetermine the concentration of an analyte.

BACKGROUND

Medical conditions such as diabetes require a person afflicted with thecondition to regularly self-monitor that person's blood-glucoseconcentration level. The purpose of monitoring the blood glucoseconcentration level is to determine the person's blood glucoseconcentration level and then to take corrective action, based uponwhether the level is too high or too low, to bring the level back withina normal range. The failure to take corrective action may have seriousmedical implications for that person.

One method of monitoring a person's blood glucose level is with aportable testing device. The portable nature of these devices enablesusers to conveniently test their blood glucose levels at differentlocations. One type of device utilizes an electrochemical test sensor toharvest and analyze the blood sample. The test sensor typically includesa capillary channel to receive the blood sample and a plurality ofelectrodes. Some electrochemical test sensor devices have largercapillary channels than are optimally desired. The bigger the capillarychannel, the more blood from a person is required to fill the channel.Because drawing blood from a person is unpleasant, it would also bedesirable to reduce the size of the capillary channel to require lessblood. However, there must be sufficient blood to cover and activate theplurality of electrodes used in an electrochemical test sensor. Thus,there exists a need for an electrochemical test sensor with a smallercapillary channel without sacrificing the accuracy of the analyteconcentration determination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an electrochemical test sensoraccording to an embodiment.

FIG. 1B is a perspective view of an electrochemical test sensoraccording to another embodiment.

FIG. 2A is a perspective view of an electrode assembly according to anembodiment.

FIG. 2B is a top view of the electrode assembly of FIG. 2A.

FIG. 2C is a bottom view of the electrode assembly of FIG. 2A.

FIG. 2D is a front view of electrochemical test sensor of FIG. 1A.

FIG. 2E is a top view of the reaction channel of an electrochemical testsensor of FIG. 1A.

FIG. 3A is a perspective view of an electrode assembly according toanother embodiment.

FIG. 3B is a top view of an electrochemical test sensor according to anembodiment.

FIG. 3C is a bottom view of an electrochemical test sensor according toan embodiment.

FIG. 4 is a top view of an electrochemical test sensor according to anembodiment.

FIG. 5 is a perspective view of an electrochemical test sensor with alancet mechanism according to an embodiment.

FIG. 6 is a perspective view of an electrochemical test sensor with anintegrated lancet mechanism according to an embodiment.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The present invention is directed to an electrochemical test sensor thatis adapted to be placed into a meter or an instrument and assist indetermining an analyte concentration in a body fluid sample. The presentelectrochemical sensor assists in reducing the volume of the fluidsample needed to properly determine the analyte concentration. The bodyfluid sample may be collected with a lancing device with which theelectrochemical sensor is coupled thereto or integrated therewith.

Examples of the types of analytes that may be collected include glucose,lipid profiles (e.g., cholesterol, triglycerides, LDL and HDL),microalbumin, hemoglobin Al_(C), fructose, lactate, or bilirubin. It iscontemplated that other analyte concentrations may also be determined.It is also contemplated that more than one analyte may be determined.The analytes may be in, for example, a whole blood sample, a blood serumsample, a blood plasma sample, other body fluids like ISF (interstitialfluid) and urine, and non-body fluids. As used within this application,the term “concentration” refers to an analyte concentration, activity(e.g., enzymes and electrolytes), titers (e.g., antibodies), or anyother measure concentration used to measure the desired analyte.

FIG. 1A illustrates a perspective view of an electrochemical test sensorin accordance with an embodiment. FIG. 1B is a perspective view of anelectrochemical test sensor according to another embodiment. As shown inFIG. 1A, an electrochemical test sensor 100 includes a housing 102having a meter-contact end 104, a front opening end 106, and anelectrode assembly 108 positioned within the housing 102. As shown inFIGS. 1A and 1B, the housing 102 is generally cylindrical in shape,whereby at least a portion of the housing 102 (desirably at the frontopening end) may have a cross-sectional shape such as circular (FIG.1A). The housing may have a rectangular cross-sectional shape such asshown with housing 102′ (FIG. 1B). It is contemplated that the housingmay have other polygonal or non-polygonal cross-sectional shapes.

The electrode assembly 108 is shown in FIGS. 1A and 1B within theinterior of the housing 102, whereby at least a portion of the assembly108 is configured to separate the interior of the housing into distinctcapillary channels 122, 124 (see also FIG. 2D). A reaction channel 109(FIG. 1A) is shown as the volume within the housing 102 that surroundsthe tip (described below) of the electrode assembly's front end 101(FIG. 2A). In an embodiment, the front end 101 of the electrode assembly108 is located inward a set distance from the front opening end 106 suchthat the reaction channel 109 occupies the space between the frontopening end 106 and the front end 101 of the electrode assembly 108. Itis contemplated that the front end of the electrode assembly may bepositioned differently with respect to the front opening end of thereaction channel. For example, a front end of the electrode assembly maybe flush with the front opening end of the housing. In another example,a front end of the electrode assembly may extend outwardly from thefront opening end and, thus, would be exposed outside the housing. In afurther example, the length of the housing 102 may be smaller thandepicted in FIG. 1 a as long the length of the housing is sufficient toallow the sample to travel from the sensor tip. In operation, the user'sfluid sample is received within the reaction channel 109 wherein analytein the fluid sample reacts with the electrodes of the electrode assemblyand is then used to determine analyte concentration in the sample.

FIG. 2A illustrates a perspective view of the electrode assembly inaccordance with an embodiment. FIGS. 2B and 2C show respective top andbottom views of the electrode assembly shown in FIG. 2A. As shown inFIG. 2A, the electrode assembly 108 includes a substrate 110 having afirst surface 112 and a second surface 114, a working electrode 116 anda counter electrode 118. The working electrode 116 is disposed on thefirst surface 112 and the counter electrode 118 is disposed on thesecond surface 114. The working electrode 116 and counter electrode 118are thus disposed on opposing surfaces of the substrate and areeffectively in a back-to-back configuration with respect to thesubstrate 110. This is further shown in FIG. 2B in which the workingelectrode 116 is shown exposed when viewing the assembly 108 from oneside, whereas the counter electrode 118 is shown exposed when theelectrode assembly 108 is flipped onto the opposing side (see FIG. 2C).

As shown in FIG. 2C, the electrode assembly 108 desirably has a uniformwidth dimension W along a substantial portion of its length, howeverthis is not necessary. In this embodiment, the width dimension W issubstantially equal to the inside diameter or width dimension of thehousing 102. By having such a width dimension, the electrode assembly108 affectively separates the interior of the housing into a firstcapillary channel 122 and a second capillary channel 124 in FIG. 2D,except desirably proximal to the tip. The back-to-back configuration ofthe working and counter electrodes 116, 118 is advantageous in thisembodiment, because the electrodes 116, 118 may effectively operatewhile minimizing the amount of required capillary space to perform theanalysis on the fluid sample. This, in turn, allows the electrodeassembly 108 to effectively perform the analysis on a smaller amount offluid sample.

As shown in FIGS. 2B and 2C, the electrode assembly 108 has two sides113 a, 113 b and also two tapering sides 111 a, 111 b between points 117a, 117 b and the front end 101. This entire front portion of theelectrode assembly 108 between points 117 a, 117 b and the front end 101is generally referred to as the tip of the electrode assembly 108. Asshown in FIGS. 2A-2C, the front end 101 is a relatively straight edge,although this is not necessary. As stated above, the reaction channel109 is the volume within the housing 102 that surrounds the tip of theelectrode assembly 108. The sides 111 a, 111 b of the electrode assembly108 desirably abut in inside surface of the tube 102, as shown in FIG.2D. This configuration creates a working area that links or allows fluidcommunication between the two capillary channels 122, 124 near the frontopening 106 of the housing as shown in FIG. 2E. This configurationassists in increasing capillary action of the fluid as it is received bythe sensor.

It is contemplated that the front end may alternatively be a pointedend, a rounded edge or other shapes. It should be noted that it is notrequired that both sides 111 a, 111 b of the electrode assembly 108taper toward one another. It is contemplated that only one side may bestraight while the other opposing side is configured at an angle. Inanother embodiment, the tip may have other appropriate shapes such assemicircular, bow-tie, and the like that desirably increase capillaryaction of the fluid received between the two channels.

The working electrode 116 and the counter electrode 118 assist inelectrochemically determining the analyte concentration of the receivedfluid sample. In one embodiment, the working electrode 116 and thecounter electrode 118 may be made from conductive material including,but not limited to, carbon, gold, platinum, ruthenium, rhodium,palladium or combinations thereof. The electrodes typically connect withthe meter contact area using an electrode pattern. The electrode patternmay include test-sensor contact and conductive leads. The workingelectrode area is less than 1.0 mm² and desirably about 0.5 or 0.6 mm²or even 0.3 mm². The electrodes may be formed by techniques such asscreen printing, sputtering, laser ablation, combinations thereof orother manufacturing methods.

The substrate may be made of polymeric materials including but notlimited to polyethylene terephthalate (PET), polysterene, polyimide,polycarbonate and combinations thereof. The housing 102 may be made ofpolymeric materials such as polyvinyl chloride (PVC) and the like. Thehousing may be made of metallic materials and alloys such as, forexample, nickel-titanium alloy or nitinol. Nitinol may be desirablebecause of its shape memory and superelasticity. The interior of thehousing may include a hydrophilic coating to increase the fill rate ofthe liquid sample into the capillary channels.

A reagent is desirably disposed on the working electrode 116 in FIG. 2B.A reagent may additionally or alternatively be disposed on the counterelectrode 118 in FIG. 2C. In particular, the reagent is located along aportion of or the entire surfaces of one or more of the electrodes 116,118. The reagent converts an analyte (e.g., glucose) in the fluid testsample, stoichiometrically into a chemical species that iselectrochemically measurable, in terms of electrical current itproduces, by the components of the working electrode 116 and the counterelectrode 118. The reagent typically includes an enzyme and an electronacceptor. The enzyme reacts with the analyte to produce mobile electronson the working and counter electrodes 116, 118. For example, the reagentlayer may include glucose oxidase, glucose dehydrogenase (GDH), and/or asurfactant if the analyte to be determined is glucose. The enzyme in thereagent layer may be combined with a hydrophilic polymer such aspoly(ethylene oxide) or other polymers such as polyethylene oxide (PEO),hydroxyethyl cellulose (HEC), carboxymethylcellulose (CMC) and polyvinylacetate (PVA). The electron acceptor (e.g., ferricyanide salt) carriesthe mobile electrons to the surface of the working electrode 116.Amperometry detection methods and gated amperometry detection methodsmay be applied to analyze the sample. Other diffusional electronmediators, such as ferrocene derivatives, conducting organic salts(tetrathiafulvalene-tetracyanoquinodimethane, TTF-TCNQ),hexamineruthenium (III) chloride, quinone compounds, transition-metalcomplexes, and phenothiazine and phenoxazine compounds, are particularlyuseful to electrically contact glucose oxidase.

The electrode assembly 108 desirably includes underfill electrodes 120,which are located on one or both surfaces of the substrate 110. It iscontemplated that an electrochemical sensor may include other electrodessuch as an underfill electrode, hematocrit-detection electrode. As shownin FIGS. 2A-2C, the electrode assembly 108 includes a pair of underfillelectrodes 120 that are located on the first and/or second substratesurfaces 112, 114, whereby the pair of underfill electrodes 120 areadjacent located between the sides 113 a, 113 b of the assembly 108 andthe center sections 115 a, 115 b of the respective electrodes 116, 118.

In particular, as shown in FIG. 2B, underfill electrode 120 a is locatedbetween the side 113 a and the center section 115 a, whereas anotherunderfill electrode 120 b is located between side 113 b and the centersection 115 a. Regarding the opposing side, as shown in FIG. 2C,underfill electrode 121 a is located between the side 113 b and thecenter section 115 b, whereas the other underfill electrode 121 b islocated between side 113 a and the center section 115 a. It iscontemplated in another embodiment that only one underfill electrode120, instead of a pair, be located on either or both surfaces of thesubstrate.

FIGS. 3A-3C illustrate an alternative electrode assembly 200 inaccordance with another embodiment. The assembly 200 includes asubstrate 201 having a first side 201A and a second side 201B. A workingelectrode 202 is shown disposed on the first side 201A and a counterelectrode 204 are disposed on the opposing second side 201B.Additionally, a first underfill electrode 206 is disposed adjacent tothe working electrode 202 on the first side 201A. A second underfillelectrode 208 is disposed adjacent to the counter electrode 204 on thesecond side 201B of the substrate 201.

As shown in the perspective view of FIG. 3A, the working electrode 202having a generally L-shaped configuration, whereby the underfillelectrode 206 is located adjacent to the working electrode 202 andoccupies the remainder of the first side 201A of the substrate. Inaddition, the counter electrode 204 on the second side 201B of thesubstrate has a generally L-shaped configuration along with thecorresponding underfill electrode 208.

In particular, the underfill electrodes 206, 208 on the opposingsurfaces of the substrate 201 are inverted with respect to one another.As shown in FIG. 3A, the L-shaped working electrode 202 is located onthe right side of the electrode assembly 200 (as viewed from the arrow99), whereas the L-shaped counter electrode 204 is located on the leftside of the electrode assembly 200 (as viewed from the arrow 99).

FIGS. 3B and 3C illustrate the opposing surfaces of the electrodeassembly 200 within a housing 210. As shown in FIGS. 3B and 3C, theunderfill electrodes 206 (FIG. 3B) and 208 (FIG. 3C) appear on the sameside laterally with respect to the corresponding electrode 202, 204. Itis contemplated, however, that the underfill electrodes may mirror oneanother and are not inverted such that they are laterally located in thesame area on opposing sides of the substrate.

FIG. 4 illustrates an electrochemical test sensor in accordance withanother embodiment. As shown in FIG. 4, the electrochemical test sensor300 includes a housing 302 with a front opening end 312. An electrodeassembly 304 is positioned within the housing 302 and includes a tip 306proximal to the front opening end 312 of the housing 302.

As shown in FIG. 4, an underfill electrode 308 is located approximatelycentrally along the surface of the electrode assembly 304. The underfillelectrode 308 includes a main body 312 and an extension leg 310 whichextends toward the tip 306 of the electrode 304. The extension leg 310desirably has a width dimension smaller than the main body 312 of theunderfill electrode 308. It is contemplated that the other side of theelectrode assembly 304 may have a similar configuration to that shown inFIG. 4, although it is not necessary. It should be noted that the aboveconfigurations of the underfill electrodes on the electrode assembly areexamples and other designs, orientations, layouts and positions arecontemplated.

It is contemplated that the sensors may be used to detect more than oneanalyte using modifications of the embodiments discussed above. In suchan embodiment, an additional working electrode would be added to thesensor on an opposing side of the existing working electrode. Thereagents to be used on the respective working electrode would beappropriately selected to assist in determining the concentrations ofthe desired analytes. Thus, two different analyte concentrations may bedetermined using one sample. In this embodiment, the counter electrodemay be used in conjunction with each of the working electrodes. Inanother embodiment, a separate counter electrode may be formed on anopposing side of the existing counter electrode.

FIG. 5 illustrates a perspective view of the above described sensorconfigured for use with a lancet mechanism in accordance with anembodiment. As shown in FIG. 5, a sensor-lancet assembly 400 includesthe sensor 402 and a lancet mechanism 404 removably coupled to thesensor 402. In particular, the sensor 402 includes the sensor assembly406 positioned within the housing 408, in which an electrode tip 410 ofthe sensor assembly 406 is positioned within a lancet interface 412coupled to the end of the housing 408.

The lancet mechanism 404 includes a lancet adapter 414 and a lancetneedle 416 extending from the lancet adapter 414. The lancet adapter 414holds the lancet needle in place and also interfaces with the lancetinterface 412 of the sensor 402. The lancet needle 416 punctures theuser's skin to obtain a fluid sample that will be collected. Althoughnot required, the adapter and interfaces may be configured to allowselective removal and replacement of the lancet mechanism from thesensor.

The lancet adapter 414 is desirably configured to be in communicationwith the lancet needle 416 and the tip 410 of the sensor 402 such thatthe fluid sample travels from the lancet needle 416 through the lancetadapter 414 to be received at the sensor tip 410. It is desirable thatthe electrode tip 410 is precisely positioned within the interface 412to ensure that it receives a predetermined sample volume. It is alsocontemplated that the sensor may alternatively be incorporated insidethe lancet needle in an embodiment. Although one particular type ofelectrode sensor 400 is shown in FIG. 5, it should be noted that any ofthe above described sensor embodiments may be used with the lancetdevice described herein.

FIG. 6 illustrates a schematic of an integrated sensor and lancetmechanism in accordance with another embodiment. As shown in FIG. 6,integrated sensor/lancet 500 has a housing 502 and a sensor 504 locatedwithin the housing 502. The housing 502 forms an opening 507. The sensor504 includes a tapered tip 506 that extends out from the opening 507 andforms a sharp end 508. Thus, the portion of the sensor 500 exposedoutside of the housing 502 functions as a lancet needle 510. As shown inFIG. 6, the lancet needle 510 desirably includes a sample transportchannel 512 that terminates at an aperture at (or proximal to) the sharpend 508 of the needle 510. The transport channel 512 is configured to bein communication with the tapered tip 506 of the sensor 504 and isdesirably treated with a hydrophilic material such that the sampleautomatically travels upward from the incision site directly to thesensor 504 without the need for any additional components orattachments.

In operation, the integrated sensor/lancet 500 extends toward the user'sskin, whereby the needle 510 makes a small incision in the skin. Thefluid sample desirably flows upward via the channel 512 to the taperedarea 506. It is desirable that the tapered area 506 is preciselypositioned within the housing 502 to ensure that it receives apredetermined sample volume. Although one particular type of electrodesensor 504 is shown in FIG. 6, it should be noted that any of the abovedescribed sensor embodiments may be used with the lancet assemblydescribed herein.

In another embodiment, the integrated sensor/lancet 500 of FIG. 6 may bemodified for use in a continuous glucose-monitoring (CGM) system. Insuch an embodiment, the integrated sensor/lancet may be simplified byeliminating unnecessary items such as the housing 502, resulting in asystem without a sample transport channel 512 being formed. In acontinuous glucose monitoring embodiment, the underfill detectionelectrodes are not necessary. The continuous glucose-monitoring systemincludes a working electrode on one side and a counter electrode on theopposing side as discussed above. The working electrode in thisembodiment may be formed of, for example, platinum or gold and thecounter electrode may be formed of, for example, silver/silver chloride.It is contemplated that other materials may be used in forming theelectrodes to be used in the glucose-monitoring system. A tapered tip inthe continuous glucose-monitoring system would extend out to form asharp end that assists in inserting the modified integratedsensor/lancet into the skin.

In one or more of the above embodiments, the working electrode desirablyhas a surface area of approximately 0.6 mm² or less. It is alsodesirable for the working electrode to use a sample volume between andincluding 0.1 and 0.3 μL, and desirably from about 0.15 to about 0.2 μL,although other sample volumes are contemplated. It is contemplated thatthe sample size may even be smaller such as from about 0.05 to about 0.3μL, and desirably from about 0.05 to about 0.2 μL.

While the invention is susceptible to various modifications andalternative forms, specific embodiments and methods thereof have beenshown by way of example in the drawings and are described in detailherein. It should be understood, however, that it is not intended tolimit the invention to the particular forms or methods disclosed, but,to the contrary, the intention is to cover all modifications,equivalents and alternatives falling within the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. An electrochemical test sensor for detecting theconcentration of an analyte in a fluid sample, the electrochemical testsensor comprising: a housing having a first end and a second opposingend, the housing including an opening at the first end to receive afluid test sample; and an electrode assembly including a substrate, aworking electrode, a counter electrode and a reagent, the substratehaving a first surface and an opposing second surface, the workingelectrode being disposed on the first surface of the substrate, thecounter electrode being disposed on the second surface of the substrate,the electrode assembly being positioned within the housing to define areaction channel.
 2. The electrochemical test sensor of claim 1, whereinthe electrode assembly extends across a width dimension of an interiorof the housing to form a first capillary channel being exposed to theworking electrode and a second capillary channel being exposed to thecounter electrode.
 3. The electrochemical test sensor of claim 2,wherein the electrode assembly includes first and second sides locatedbetween first and second surfaces, the first and second sides at one endbeing tapered toward each other.
 4. The electrochemical test sensor ofclaim 2, wherein the first and second capillary channels are incommunication with one another at the reaction channel.
 5. Theelectrochemical test sensor of claim 1, further comprising at least oneunderfill electrode disposed on at least one of the first and secondsurfaces of the substrate.
 6. The electrochemical test sensor of claim5, wherein the at least one underfill electrode includes an underfillelectrode located on the first and second surfaces of the substrate. 7.The electrochemical test sensor of claim 1, wherein a volume of thereaction channel is from about 0.1 μL to about 0.3 μL.
 8. Theelectrochemical test sensor of claim 1, wherein a volume of the reactionchannel is less than 0.5 μL.
 9. The electrochemical test sensor of claim1, wherein a volume of the reaction channel is less than 0.3 μL.
 10. Theelectrochemical test sensor of claim 1, wherein a volume of the reactionchannel is from about 0.1 μL to about 0.5 μL.
 11. The electrochemicaltest sensor of claim 1, wherein the housing at a first end has acircular cross-sectional shape.
 12. A method for determining theconcentration of an analyte in a fluid sample with a test sensor, themethod comprising: providing an electrochemical test sensor including ahousing and an electrode assembly, the housing having a first end and asecond opposing end, the housing including an opening at the first endto receive a fluid test sample; the electrode assembly including asubstrate, a working electrode, a counter electrode and a reagent, thesubstrate having a first surface and an opposing second surface, theworking electrode being disposed on the first surface of the substrate,the counter electrode being disposed on the second surface of thesubstrate, the electrode assembly being positioned within the housing todefine a reaction channel; providing the fluid sample to the reactionchannel; reacting the analyte of the fluid sample with the reagent togenerate an electrical signal in the sensor in response to the presenceof the analyte in the fluid sample; and determining the analyteconcentration using the electrical signal.
 13. The method of claim 12,wherein the electrode assembly extends across a width dimension of aninterior of the housing to form a first capillary channel being exposedto the working electrode and a second capillary channel being exposed tothe counter electrode.
 14. The method of claim 13, wherein the first andsecond capillary channels are in communication with one another at thereaction channel.
 15. The method of claim 13, wherein the electrodeassembly includes first and second sides located between first andsecond surfaces, the first and second sides at one end being taperedtoward each other.
 16. The method of claim 12, wherein a volume of thereaction channel is from about 0.1 μL to about 0.3 μL.
 17. An integratedlancet/electrochemical test sensor assembly for detecting theconcentration of an analyte in a fluid sample, the assembly comprising:a housing having a first end and a second opposing end, the housingincluding an opening at the first end to receive a fluid test sample;and an electrode assembly including a substrate, a working electrode, acounter electrode and a reagent, the substrate having a first surfaceand an opposing second surface, the working electrode being disposed onthe first surface of the substrate, the counter electrode being disposedon the second surface of the substrate, the electrode assembly beingpositioned within the housing to define a reaction channel; anintegrated lancet extending from the tapered area and exposed outside ofthe opening, the lancet needle including a fluid channel thereinconfigured to pass the fluid sample from an incision site to the taperedarea via capillary action.
 18. An electrochemical test sensor assemblyfor detecting the concentration of an analyte in a fluid sample, theelectrochemical test sensor comprising: a lancet mechanism including ahollow lancet adapter and a needle configured to flow the fluid sampletherethrough; a housing having a first end and a second opposed end, thesecond end coupled to the hollow lancet adapter, the housing includingan opening at the first end to receive the fluid sample received fromthe lancet needle, the housing coupled to the lancet mechanism; anelectrode assembly including having a first surface and an opposedsecond surface, the electrode assembly including a working electrodedisposed on the first surface of the substrate and a counter electrodedisposed on the second surface of the substrate, the working and counterelectrode having a tip proximal to the opening, wherein the electrodeassembly is positioned within the housing and configured to define areaction channel located between the opening of the housing and the tipof the electrode assembly.